Glass gobos and 360Q not friends?

[CrazyTechie]

So for our production of Equus at my college I was given the task of ME. Well the light plot called for some glass gobos to be used in some 360Q 6x9's. It wasn't too long into rehearsals we started having some problems with the gobos falling apart like so:

So my question is, why does this happen in a 360Q but not in a S4? All the ones in the S4s were still in perfect condition when I took them out to put away today.

 

[derekleffew]

Rosco Gobos - Fixture Size Chart

 

[CrazyTechie]

Thanks for that information, I'm sure it will come in handy.
Here is the link for the same chart but with ETC's lights Rosco Gobos - Fixture Size Chart.

I'd still like to know what causes the gobo to break apart in the fixture if anyone knows.

Thanks.

 

[Les]

It's because the 360Q has an Alzak aluminum reflector which transmits a lot more heat through the beam than the glass Dichroic reflector found in a Source Four. The Dichroic reflector passes heat through the rear of the fixture, while the aluminum reflector throws it forward and through the gate. This causes the 360Q gate to get way hotter than the glass gobo is designed to handle, in turn, breaking it apart. I've also seen the rear lens in a 6x9 crack in a Y formation, and I've even pulled a gobo out of a poorly bench focused 6x12 to find that it is red hot.

It's too bad your professor apparently hasn't covered this in class.

 

[jglodeklights]

Ditto on what Les said. To expand on what was already said about Dichroic reflectors, how they work is by acting as a cut-off filter. If you've ever done infrared photography, you know that generally you utilize a lens filter that allows only infrared light to pass through it. Unlike that filter which simply absorbs non-IR spectrum light waves, Dichroic reflectors shove it out the front of the lighting unit. Not only are they used in more current fixtures, but every MR-16 lamp is comprised of the lamp and a Dichroic reflector around it.

Also worth mentioning is the transmission efficiency of the lens train in a 360Q. S4 units use thinner, more pure glass and thus; especially those with 19, 26 and 50 degree lens tubes mounted because they only have one lens versus two; allow more light to pass through without it being blocked or reflected back into the unit. Physics dictates that energy has to go somewhere, and if light isn't going out the front of the unit then it is turning into heat within it.

 

[Lotos]

I'm late to the party, and can't really add much... But, to test this yourself, the following experiment is handy:

Plug in a Source 4 and an Altman 360Q in a convenient to reach location.
Lamp them both roughly the same.
IE: 575w HPL in the S4, and a GLC or and old HP600 in the Altman.

Turn them on for 15-20 minutes or so, then go up and (gently... You want to keep your skin here) touch the sides of the barrel's on both...

 

[jglodeklights]

I'm late to the party, and can't really add much... But, to test this yourself, the following experiment is handy:

Plug in a Source 4 and an Altman 360Q in a convenient to reach location.
Lamp them both roughly the same.
IE: 575w HPL in the S4, and a GLC or and old HP600 in the Altman.

Turn them on for 15-20 minutes or so, then go up and (gently... You want to keep your skin here) touch the sides of the barrel's on both...

Maybe getting two thermometers rather than using your hand would be wise.......

 

[Lotos]

Maybe getting two thermometers rather than using your hand would be wise.......

Oh that's just crazy talk

 

[CrazyTechie]

It's too bad your professor apparently hasn't covered this in class.

Our TD who is also our LD knew that this might happen but we were out of S4's so he had to go with the 360Q's. Thanks for the explanation it really helps and is something I haven't learned yet in the very few amount of theatre classes I've taken so far.

Turn them on for 15-20 minutes or so, then go up and (gently... You want to keep your skin here) touch the sides of the barrel's on both...

Maybe getting two thermometers rather than using your hand would be wise.......

Not a bad idea to test out, unfortunately I don't think I have a thermometer lying around to use. Good thing I have ten fingers, I think I can sacrifice one or two for the sake of knowledge and still be able to work.

 

[jglodeklights]

Oh, you won't be sacrificing your fingers.....just your fingerprints!

 

[Lotos]

Oh, you won't be sacrificing your fingers.....just your fingerprints!

Never trust a lighting technician who still has recognizeable fingerprints...
Or is it the other way around? I can never remember...

 

[CrazyTechie]

So today the costumes and makeup class came in to see makeup under stage lights and I was able to find a 360Q and a S4 that had been on for a while and I touched both of them. Well the 360Q was much hotter than the S4 so now the reasoning behind all of this is starting to make sense.

 

[derekleffew]

From KnowledgeBase: Source Four Heat Ratings/ How Much Heat Does the Source 4 Emit? - Electronic Theatre Controls :

What is the Gate Temperature of a Source Four ERS?
In a test condition created by placing one shutter blade into gate covering 1/2 of field, and
placing the thermal probe on the backside (shaded) of the shutter, the maximum S4 gate temps
(A-size) were recorded as follows:

HPL 575w/115v/300hr = 622°F
HPL 750w/115v/300hr = 786°F

Anyone wanna stick a thermal probe in a 360Q and post the results?

 

[Lotos]

Out of curiosity, now that I think about it...
You didn't do something silly like put FEL's in those Altmam 360Q's as well, did you?

Not that the GLC will be gentle and kind to the Gobo's... But FEL's are notorious heat monsters.

 

[CrazyTechie]

Out of curiosity, now that I think about it...
You didn't do something silly like put FEL's in those Altmam 360Q's as well, did you?.

Heavens no. I've never heard anything but bad about FEL's. All the 360Q had some variant of HX60n (n is any number in that series).

Anyone wanna stick a thermal probe in a 360Q and post the results?

If only I had or knew where to get one of those...I shall do a quick Google search.

 

[derekleffew]

I was going to do it, but my infrared thermometer only goes to 250°C, so that's pointless.

I wonder if Kelite would have this information handy? One would think Apollo has done lots of testing of gobos in various instruments.

 

[CrazyTechie]

I was going to do it, but my infrared thermometer only goes to 250°C, so that's pointless.

Sad day. I have some potential good news. My dad has a multimeter that also has a temperature probe that will go up to 1,832˚F. Its this one in particular Amazon.com: Digital Multimeter 7 Function (623-GDT-200A) Category: Clamp Meters and Multimeters: Home Improvement

So next question, how long should I leave the light on before I touch the probe to the shutter?

 

[gafftapegreenia]

I've gotta tell ya, the lamp/reflector housing of a Source 4 still gets pretty freakin' expletive hot. Thank ETC they put the plastic handles on the 750 caps.

 

[CrazyTechie]

I've gotta tell ya, the lamp/reflector housing a a Source 4 still gets pretty freakin' expletive hot. Thank ETC they put the plastic handles on the 750 caps.

For sure I will second that as I found out today. And I've still got my fingerprints which is always good!

 

[derekleffew]

...So next question, how long should I leave the light on before I touch the probe to the shutter?

With the lamp at 100%, do a test at 5, 10, and 15 minutes. I doubt there will be much if any difference. Let us know. Also make sure to tell us the lamp type and wattage, and the voltage applied. Use applicable PPE, and be sure to read, understand, and follow all safety instructions that came with your meter.

I've gotta tell ya, the lamp/reflector housing of a Source 4 still gets pretty freakin' expletive hot. ...

Not as hot as the heat sink on a freakin' expletive Selecon Pacific!